CN101288253A - System and method for spreading and scrambling downlink physical channels - Google Patents

Abstract

The present invention discloses a method for reducing the number of channels required in a transmission system employing multiple channels to communicate with multiple receiving stations. The method comprises the steps of: dividing said plurality of channels into a plurality of groups, each group comprising a group of channels; and partially spreading and combining said groups of channels within each respective group into A new group channel.

Description

Systems and methods for spreading and scrambling downlink physical channels

priority information

This application claims priority to operative application Ser. No. 11/175,664, filed July 6, 2005, the contents of which are hereby incorporated by reference in their entirety.

background

The present invention relates generally to communication systems, and more particularly to transmission systems for mobile communication systems.

Certain cellular mobile communication systems employ multiplexing techniques such as Wideband Code Division Multiple Access (WCDMA) to provide frequency efficiency and reduce interference at receiving stations such as mobile units. In a cellular mobile communication system employing WCDMA, each signal to be transmitted from a base station is spread over a wide bandwidth at the base station using a unique spreading code. Each mobile unit despreads one of the wide bandwidth signals back to the original signal using a copy of the spreading code used to spread the original signal. Wide bandwidth signals spread with different spreading codes are not despread at the mobile device.

For example, U.S. Published Patent Application 2002/0150065 discloses a Universal Mobile Telecommunications System (UMTS) using frequency division multiplexing (FDD) mode, where the base station includes a transmitter and transmits signals including a spreader and a scrambler processing unit. It is disclosed that each signal will be multiplied with a spreading code unique to a particular mobile device. Each of the transmitted signals is also scrambled by a scrambling code, wherein the scrambling code is unique to that base station.

U.S. Patent No. 6,665,228 discloses a method for reducing synchronization code interference in a WCDMA communication system, in part by transmitting information on additional channels to reduce interference attributable to synchronization codes transmitted on different channels and device. US Published Patent Application No. 2003/0103478 discloses a system and method for determining whether a new channel requested to be established is already in use in a WCDMA communication system.

However, establishment of a new channel is not always possible if the base station cannot assign a new spreading code to the new channel. US Published Patent Application 2003/0081584 discloses a method and system for downlink channelization code assignment in UMTS, in which an Orthogonal Variable Spreading Factor (OVSF) is assigned to each new channel while maintaining the previous Assigned OVSF code. This is achieved by providing reserved codes in the generation and release of OVSF codes.

However, such transmission systems typically perform spreading over channels on a channel basis. For example, a channelization code can be uniquely described as _Cch,SF,m , where SF is the spreading factor of the code and m is the code number (0≤m≤SF-1). Each level in the code tree defines a channelization code of length SF corresponding to a spreading factor SF. Different spreading factors (eg, 4≤SF≤512) are used according to the rate of each user. As shown, for example, in Figure 1, spreading and scrambling in the downlink physical channel can generally be achieved by complex multiplexing the channels into I and Q channels first multiplied with the channelization code vector frequency. Each element of the code vector is either +1 or -1. The size of the code vector is an integer power of 2. Each pair of two consecutive symbols is first serial-to-parallel converted (at 10) and mapped (at 12) to the I branch and the Q branch. The I and Q branches are then spread to the chip rate by the same real-valued channelization code (14) at combiners 16 and 18, respectively. The value on the Q branch is then combined at 20 with the variable j, and the sequence of real-valued chips on the I and Q branches is considered as a complex-valued sequence of chips as provided at 22 . The sequence of chips is then scrambled (as shown at 24) by a complex-valued scrambling code Sdl _,n , where each element of the scrambling code vector (of the form ±1±i) is provided by combiner 26 at node 28 . The different downlink channels (as shown at 28 and 28' in FIG. 2 ) are combined at combiner 38, where each complex-valued spread spectrum channel (corresponding to points 28 and 28') passes through combiner 30 respectively. and 34 are weighted by weighting factors _Gi (eg, G ₁ as shown at 32 and G ₂ as shown at 36 ). The complex-valued P-SCH and S-SCH are weighted by weighting factors _Gp (shown at 42) and _Gs (shown at 44) by combiners 40 and 44, respectively, and the channels are all combined at 48 to combine at node A combined multi-channel output is provided at 50 . All downlink physical channels are then combined using complex addition.

In such channel by channel spread systems, however, material and processing costs are generally proportional to the number of channels. Therefore, there is a need for a more efficient and cost-effective implementation of a transmission system for a mobile communication system.

Contents of the invention

According to one embodiment, the present invention provides a method for reducing the number of channels required in a transmission system employing multiple channels to communicate with multiple receiving stations. The method comprises the steps of: dividing a plurality of channels into a plurality of groups, and each group comprising a group of channels, partially spreading and combining said groups of channels in each respective group into a new group of each respective group channel. In some embodiments, the method further comprises the steps of dividing said group channels into subgroup channels, partially spreading and combining subgroup channels, and spreading and scrambling subgroup channels. In some embodiments, the method further comprises the steps of spreading and scrambling the group channel or subgroup channel, and combining the group channel or subgroup channel for output to the transmitter node.

Brief description of the drawings

The following description can be further understood with reference to the accompanying drawings, in which:

FIG. 1 shows a schematic diagram of a spreading and scrambling system for a downlink physical channel in a communication system of the prior art;

Figure 2 shows a schematic diagram of a spread spectrum and modulation system in a prior art communication system, where different downlink physical channels are combined;

FIG. 3 shows a schematic diagram of a code tree for generating OVFS codes in a communication system according to an embodiment of the present invention;

FIG. 4 shows a schematic diagram of a spreading and scrambling system for a downlink physical channel in a communication system according to an embodiment of the present invention; and

Fig. 5 shows a schematic diagram of a spread spectrum and modulation system in a communication system according to an embodiment of the present invention, where different downlink physical channels are combined.

The figures are shown for illustration purposes only.

Detailed Description of Illustrative Embodiments

According to some embodiments, the present invention provides that the spreading and scrambling process can be broken down into multiple stages. In each stage, channels are divided into several groups. Within each group, the channels in that group are partially spread and combined into new channels. As a result, fewer channels exist in the next stage. Partial spreading and combining operations are repeated in all stages except the last stage. In the final stage, the newly formed channel from the previous stage is spread, scrambled and combined into one data stream to be sent to the radio frequency (RF) processing unit. Partial spreading and combining techniques reduce the number of effective channels in all spreading/scrambling processes, thus lowering the overall processing cost. If the number of channels N is large, the system can reduce the processing cost to the original 4/N. For example, if the number of downlink channels is equal to 100 (eg, in typical voice applications), the processing cost can be reduced by 1/25 (or by 95%). In voice applications in UMTS-FDD of WCDMA, spreading and scrambling can account for most of the processing cost in the downlink.

According to one example, the system of the present invention may provide a first stage in which part of the spread spectrum channels in the subtree rooted at C _Ch,8,k are combined to have channelization codes C _Ch,8,k (k=0 to the equivalent channel of 7). A gain value _Gi is then applied to the input channel. Input channels can have different gain values. In the second stage, eight equivalent channels C _Ch,8,k (k=0 to 7) are again spread, scrambled and combined. The method of the present invention can be applied to many additional stages.

表示克罗内克积(Kronecker product)，运算mod(x，y)表示x除y的余数。具体地，第一群，例如，C_ch，256，n(未示出)由 $C_{\mathrm{ch},256,n}=C_{\mathrm{ch},8,k}\⊗C_{\mathrm{ch},32,\mathrm{mod}(n,32)}$ 提供。然后关于第一群的该乘积由扩频器利用一个码元扩频，以为包括32个码元的第一群提供输出。第二群，例如，C_ch，128，p(未示出)由 $C_{\mathrm{ch},128,p}=C_{\mathrm{ch},8,k}\⊗C_{\mathrm{ch},16,\mathrm{mod}(p,16)}$ 提供。然后关于第二群的该乘积由扩频器利用两个码元扩频，以为包括32个码元的第二群提供输出。部分扩频码由C_{ch，32，mod(n，32)}和C_{ch，16，mod(p，16)}提供。然后有关第一和第二群C_ch，8，k)的输出的残差扩频码被组合，以利用32个码元提供等价信道化码(C_ch，8，k)。For example, as shown in FIG. 3 , an OVSF code tree 52 according to an embodiment of the present invention may include nodes C _ch,8,k ( 54 ) provided by a first group 56 and a second group 58 . Since up to 8 channels can be spread using C _ch,8,k (k=0 to 7), each channelization code can be formed by C _ch,8,k , so part of the spreading code can be given by $C_{\mathrm{ch},\mathrm{SF},m}=[C_{\mathrm{ch},8,k}\±$ $C_{\mathrm{ch},8,k}\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\±C_{\mathrm{ch},8,k}]=C_{\mathrm{ch},8,k}\⊗C_{\mathrm{ch},\mathrm{SF}/8,\mathrm{mod}(m,\mathrm{SF}/8)}$ to provide, where the operator

Represents the Kronecker product, and the operation mod(x, y) represents the remainder of x divided by y. Specifically, the first group, e.g., C _ch,256,n (not shown) consists of $C_{\mathrm{ch},256,\mathrm{no}}=C_{\mathrm{ch},8,k}\⊗C_{\mathrm{ch},32,\mathrm{mod}(\mathrm{no},32)}$ supply. This product for the first group is then spread by a spreader with one symbol to provide an output for the first group comprising 32 symbols. A second group, e.g., C _{ch, 128, p} (not shown) consists of $C_{\mathrm{ch},128,p}=C_{\mathrm{ch},8,k}\⊗C_{\mathrm{ch},16,\mathrm{mod}(p,16)}$ supply. This product for the second group is then spread by the spreader with two symbols to provide an output for the second group comprising 32 symbols. Part of the spreading code is provided by C _{ch, 32, mod(n, 32)} and C _{ch, 16, mod(p, 16)} . The residual spreading codes on the outputs of the first and second groups C _ch,8,k are then combined to provide an equivalent channelization code (C _ch,8,k ) with 32 symbols.

Partial spreading and combining is shown in Figure 4, where each pair of two consecutive symbols is first serial-to-parallel converted (at 60) and then mapped (at 62) and weighted by a weighting factor G as shown at 64 . Then, apply partial spreading code C _{ch, SF/8, mod(m, SF/8) as} shown in 66, and carry out similar processing (as shown in 68 and 70) to the remaining channel of this group and in 72 combine at node 74 to provide a group output for group _Xk , where k=0 to 7.

Further spreading, scrambling and combining of outputs 74', 74", 74'", etc. of groups _X0 - _X7 is provided as shown in FIG. Specifically, combiners 76 and 78 apply spreading and scrambling codes C _ch,8,0 and S _dl,n to group 1 (X ₀ ), while combiners 80 and 82 apply spreading and scrambling codes C _{ch , 8, 1} and S _dl,n are applied to group 2(X ₁ ). The remaining groups are similarly spread and scrambled as shown generally at 84 . The outputs of these 8 groups are then combined by combiner 86 to provide output at node 88 for the transmission system.

Those skilled in the art will appreciate that numerous modifications and changes can be made to the above-disclosed embodiments without departing from the spirit and scope of the invention.

Claims (18)

1. A method for reducing the number of channels required in a transmission system employing multiple channels to communicate with multiple receiving stations, said method comprising the steps of: dividing the plurality of channels into a plurality of groups, each group comprising a set of channels; and The sets of channels within each respective group are partially spread and combined into a new group channel for each respective group. 2. The method of claim 1, further comprising the steps of spreading and scrambling the group channels. 3. The method of claim 2, further comprising combining the group channels for output to a transmitter node. 4. The method of claim 1, further comprising the step of dividing the group of channels into subgroups of channels, each subgroup comprising a subset of channels. 5. The method according to claim 4, further comprising the step of partially spreading and combining the channels of the subgroups in each corresponding subgroup into channels of a new subgroup. 6. The method according to claim 5, further comprising the steps of spreading and scrambling said subgroup channels. 7. The method of claim 6, further comprising combining the subgroup channels for output to a transmitter node. 8. The method of claim 1, wherein the groups of channels in each group are defined by applying a spreading code $C_{\mathrm{ch},G,k}\⊗C_{\mathrm{ch},\mathrm{SF}/G,\mathrm{mod}(m,\mathrm{SF}/G)}$ to spread spectrum, where G is the number of groups. 9. The method of claim 1, wherein the plurality of channels are divided into eight groups. 10. The method of claim 9, wherein the groups of channels in each group are obtained by applying a spreading code $C_{\mathrm{ch},8,k}\⊗C_{\mathrm{ch},\mathrm{SF}/8,\mathrm{mod}(m,\mathrm{SF}/8)}$ to spread the spectrum. 11. A method for reducing the number of channels required in a transmission system employing multiple channels to communicate with multiple receiving stations, said method comprising the steps of: dividing the plurality of channels into a plurality of groups, each group comprising a set of channels; partially spreading and combining said sets of channels within each respective group into a new group channel for each respective group; dividing the plurality of group channels into a plurality of subgroups, each subgroup comprising a subset of channels; partially spreading and combining said subgroup channels within each respective subgroup into a new subgroup channel for each respective subgroup; spreading and scrambling the subgroup channels; and The subgroup channels are combined for output to a transmitter output node. 12. The method of claim 11 , wherein the plurality of group channels are divided into a plurality of subgroups, and the steps of partially spreading and combining the subgroup channels in each corresponding subgroup is repeated. 13. The method of claim 11, wherein the groups of channels in each group are defined by applying a spreading code $C_{\mathrm{ch},G,k}\⊗C_{\mathrm{ch},\mathrm{SF}/G,\mathrm{mod}(m,\mathrm{SF}/G)}$ to spread spectrum, where G is the number of groups. 14. A method for reducing the number of channels required in a transmission system employing multiple channels to communicate with multiple receiving stations, said method comprising the steps of: dividing the plurality of channels into a plurality of groups, each group comprising a set of channels; and partially spreading and combining said sets of channels within each respective group into a new group channel with respect to each respective group, wherein said sets of channels in each group are obtained by applying a spreading code $C_{\mathrm{ch},G,k}\⊗C_{\mathrm{ch},\mathrm{SF}/G,\mathrm{mod}(m,\mathrm{SF}/G)}$ to spread spectrum, where G is the base group number spreading and scrambling the final group channel; and The final group channels are combined for output to a transmitter node. 15. A system for reducing the number of channels required in a transmission system employing multiple channels to communicate with multiple receiving stations, said system comprising the steps of: dividing means for dividing the plurality of channels into a plurality of groups, each group comprising a set of channels; and Partial spreading and combining means for partially spreading and combining said groups of channels within each respective group into a new group channel for each respective group. 16. The system of claim 15, further comprising spreading and scrambling means for spreading and scrambling the group channels. 17. The system of claim 16, wherein the groups of channels in each group are defined by applying a spreading code $C_{\mathrm{ch},G,k}\⊗C_{\mathrm{ch},\mathrm{SF}/G,\mathrm{mod}(m,\mathrm{SF}/G)}$ to spread spectrum, where G is the number of groups. 18. The system of claim 17, wherein the number G of said groups is eight.

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